Using battery-backed SRAM of the onboard RTC chip

If you need your variables to survive power outages and reboots, there are 64 bytes of battery-backed memory available.

Raspbian (Linux)

You can access the SRAM via this file:

/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-006f/nvram

Just keep in mind the limit of 64 bytes.

REXYGEN

In REXYGEN, there is an internal mechanism for handling persistent variables, which stores the values on a permanent storage medium (hard drive, SD card, eMMC, etc.).

Still, you can use the SILO function block to access the SRAM via this file:

/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-006f/nvram

Keep in mind the limit of 64 bytes.

Codesys

It is recommended to use the MCP7941x library by Aliazzz.

Keep in mind the limit of 64 bytes.